1. Field of the Invention
The invention relates to an inverter that supplies alternate current (AC) power to an AC motor.
2. Description of Related Art
Inverters are provided with a capacitor that smoothes direct current (DC) voltage. The capacitor is charged using DC voltage, and is preferably discharged while the inverter is not used, or upon collision of a vehicle. For instance, an inverter that energizes a motor for travel, in an electric automobile or a hybrid automobile, is charged at high voltage. The capacitor must be discharged upon the occurrence of a collision accident or during servicing.
Japanese Patent Application Publication No. 11-318085 (JP 11-318085 A) discloses a technology in which a motor for travelling is used to discharge a capacitor. In this technology, a motor is caused to rotate, upon collision of a vehicle, using power stored in a capacitor; as a result, the electrical energy that is stored in the capacitor is dissipated by being converted to kinetic energy. That is, the capacitor is discharged.
The need to discharge the capacitor arises only in rare cases. However, discharge must take place reliably when required, although that is seldom the case, and must be tested on a routine basis. Preferably, for instance, a discharge test is performed on the capacitor at the start and at the end of the operation of the inverter, or if motor rotation is not necessary (in the case of a motor for travelling, at a period in which the shift lever is in the parking position or the brake pedal is depressed, and vehicle speed is accordingly zero), to check whether a discharge circuit is operating normally or not.
In the discharge test of the capacitor, however, causing the motor to rotate using the power stored in the capacitor may give rise to discomfort to occupants, on account of motor rotation under normal conditions, when there is no need to cause the motor to rotate. Even if braking is applied to motor, the user may still feel discomfort on account of a slight vibration from the motor, if the latter is energized.